Is it possible to send to more than 1 Data Extension with the SOAP API?

Question

We want to send out sometimes to more than one Data Extension using the SOAP API. But when we use it like this it only send out to one Data Extension not both. I think it should be possible. Our question is how.

<?xml version="1.0" encoding="UTF-8"?>
<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" 
                xmlns:ns1="http://exacttarget.com/wsdl/partnerAPI" 
                xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
    <soapenv:Header>
        <h:fueloauth xmlns="http://exacttarget.com" xmlns:h="http://exacttarget.com">ACCESS_TOKEN
        </h:fueloauth>
    </soapenv:Header>
    <soapenv:Body>
        <ns1:CreateRequest>
            <ns1:Options></ns1:Options>
            <ns1:Objects xsi:type="ns1:EmailSendDefinition">
                <ns1:CustomerKey>SEND_DEFINITION_KEY</ns1:CustomerKey>
                <ns1:Name>SEND_DEFINITION_KEY</ns1:Name>
                <ns1:Description>DESCRIPTION</ns1:Description>
                <ns1:SendClassification>
                    <ns1:CustomerKey>Default Commercial</ns1:CustomerKey>
                </ns1:SendClassification>
                <ns1:SenderProfile>
                    <ns1:CustomerKey>default</ns1:CustomerKey>
                </ns1:SenderProfile>
                <ns1:DeliveryProfile>
                    <ns1:CustomerKey>Default</ns1:CustomerKey>
                </ns1:DeliveryProfile>
                <ns1:SendDefinitionList>
                    <ns1:CustomerKey>DATAEXTENSION_DER_GRUPPE_1</ns1:CustomerKey>
                    <ns1:DataSourceTypeID>CustomObject</ns1:DataSourceTypeID>
                </ns1:SendDefinitionList>
                <ns1:SendDefinitionList>
                    <ns1:CustomerKey>DATAEXTENSION_DER_GRUPPE_2</ns1:CustomerKey>
                    <ns1:DataSourceTypeID>CustomObject</ns1:DataSourceTypeID>
                </ns1:SendDefinitionList>
                <ns1:Email>
                    <ns1:ID>EMAIL_ID</ns1:ID>
                </ns1:Email>
            </ns1:Objects>
        </ns1:CreateRequest>
    </soapenv:Body>
</soapenv:Envelope>

Answer 1

It is not currently possible to send to multiple data extensions in a single send.

It is possible to use a query activity to join together 2 data extension into a single data extension which could be used as the audience.